1. Field of the Invention
The present invention relates to a light extraction substrate for an organic light-emitting device (OLED), a method of fabricating the same and an OLED including the same, and more particularly, to a light extraction substrate for an OLED which can improve the light extraction efficiency of the OLED, a method of fabricating the same and an OLED including the same.
2. Description of Related Art
In general, light emitting devices can be generally divided into organic light-emitting devices (OLEDs) in which a light-emitting layer is made of an organic matter and inorganic light-emitting devices (ILEDs) in which a light-emitting layer is made of an inorganic matter. Among them, OLEDs are self-emitting devices which generate light as excitons that are generated through the recombination of electrons injected through a cathode and holes injected through an anode emit energy. OLEDs have a variety of advantages, such as, self-emission, a wide viewing angle, a high resolution, natural color reproduction and rapid response.
Recently, active studies are underway in order to apply OLEDs to a variety of devices, such as portable information devices, cameras, watches, office equipment, information display windows of vehicles, televisions (TVs), displays, or illumination systems.
Methods for improving the luminous efficiency of OLEDs include a method of improving the luminous efficiency of a material that constitutes a light-emitting layer and a method of improving the light extraction efficiency at which light generated from the light-emitting layer is extracted.
The light extraction efficiency depends on the refractive indices of layers which form each OLED. In a typical OLED, when a ray of light generated from the light-emitting layer is emitted at an angle greater than a critical angle, the ray of light is totally reflected at the interface between a higher-refractivity layer, such as a transparent electrode layer, and a lower-refractivity layer, such as a substrate. This consequently lowers the light extraction efficiency, thereby lowering the luminous efficiency, which is problematic.
In fact, due to this problem of total reflection at the interface, only about 25% of light generated from the light-emitting layer of an OLED is emitted outward and about 75% of the light is lost.
The information disclosed in the Background of the Invention section is provided only for enhancement of (or better) understanding of the background of the invention, and should not be taken as an acknowledgment or any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.